Borehole stress meter system and method for determining wellbore formation instability

Abstract

A Wellbore stress meter system and method for determining wellbore formation instability, comprising a first load cell, a first pressure sensor with a pressure output signal, a wireless communication system, a cable, and a surface device, said first load cell comprises; a second pressure sensor with a stress output signal, a cell element comprising a fluid, a first interface element in a first end of said first load cell with fluidly separated first and second surfaces wherein said first surface is in fluid communication with said fluid, and said first interface element moves relative said cell element as a function of a force applied on said first surface, and compresses said fluid acting on said second pressure sensor.

The invention claimed is: 
     
       1. A wellbore stress meter system comprising a first load cell, a first pressure sensor with a pressure output signal, a wireless communication system including an external device and an internal device, a cable, and a surface device, wherein said first load cell, said first pressure sensor and said external device are disposed within an investigation interval outside said wellbore conduit, and said internal device and said cable are disposed inside said wellbore conduit, wherein said first load cell includes:
 a second pressure sensor with a stress output signal; 
 a cell element comprising a first fluid with a first fluid pressure; and 
 a first interface element disposed in a first end of said first load cell with fluidly separated first and second surfaces, wherein said first surface is in fluid communication with said first fluid, and said second surface is in operable communication with solid masses in said investigation interval, and said first interface element is longitudinally movable relative said cell element as a function of a first force from said sold masses applied on said first surface relative a second end opposite said first end, and said first fluid is compressible on said second pressure sensor, wherein said second pressure sensor and said first pressure sensor are in communication with said surface device via said wireless communication system and said cable. 
 
     
     
       2. The wellbore stress meter system according to  claim 1 , wherein said cell element is fixed to said wellbore conduit. 
     
     
       3. The wellbore stress meter system according to  claim 2 , further comprising a focal stress receptacle disposed in said investigation interval, said first load cell disposed in said focal stress receptacle, wherein said focal stress receptacle is configured to act on said second surface of said first interface element with said first force when said focal stress receptacle is subject to a second force from surrounding solid masses in said investigation interval. 
     
     
       4. The wellbore stress meter system according to  claim 3 , wherein said solid masses include cement in said investigation interval and said focal stress receptacle is disposed within said cement such that said stress receptacle is subject to said second force from said cement. 
     
     
       5. The wellbore stress meter system according to  claim 1 , wherein said cell element is a cylinder and said first interface element is a piston movably disposed inside said cylinder . 
     
     
       6. The wellbore stress meter system according to  claim 1 , wherein said first interface element is a bellow or a diaphragm. 
     
     
       7. The wellbore stress meter system according to  claim 1 , wherein said second pressure sensor is a quartz pressure sensor. 
     
     
       8. The wellbore stress meter system according to  claim 1 , wherein said first pressure sensor is a quartz pressure and temperature transducer. 
     
     
       9. The wellbore stress meter system according to  claim 1 , wherein said first load cell comprises a second interface element disposed in said second end of said first load cell with fluidly separated first and second surfaces, wherein said first surface is in fluid communication with said first fluid, and said second interface element is movable relative to said cell element as a function of said first force. 
     
     
       10. The wellbore stress meter system according to  claim 1 , further comprising:
 a pressure sensor housing, including said first pressure sensor with said output pressure signal; 
 a first oil filled chamber; 
 a pressure transfer means between said first oil filled chamber and said first pressure sensor, wherein said first pressure sensor is isolated from said oil filled chamber by said pressure transfer means, and 
 a pressure permeable filter port through a wall of said housing, wherein said pressure permeable filter port is in hydrostatic connectivity with said first oil filled chamber. 
 
     
     
       11. The wellbore stress meter system according to  claim 10 , wherein said housing is integrated with said first load cell. 
     
     
       12. The wellbore stress meter system according to  claim 1 , further comprising a signal processing unit disposed in an investigation interval and in communication with said second pressure sensor, said first pressure sensor, and a communication port on said signal processing unit. 
     
     
       13. The wellbore stress meter system according to  claim 12 , wherein said signal processing unit is arranged for modulating said stress output signal and said pressure output signal onto a common carrier signal. 
     
     
       14. The wellbore stress meter system according to  claim 1 , wherein said wireless link is configured to transfer power from said surface device to said internal device, said internal device configured for generating a varying electromagnetic field from said power, and said external device is configured to provide power to said signal processing unit by power harvesting said varying electromagnetic field. 
     
     
       15. The wellbore stress meter system according to  claim 1 , comprising a second load cell disposed perpendicular to said first load cell and subject to a third force, wherein said third force is perpendicular to said first force. 
     
     
       16. The wellbore stress meter system according to  claim 1 , comprising a second load cell disposed perpendicular to said first load cell, and subject to detect a third force, wherein said third force is perpendicular to said first force, wherein said second load cell is in communication with said signal processing unit, and said signal processing unit is in communication with said communication port on said signal processing unit. 
     
     
       17. A method for determining a wellbore formation instability, the method comprising:
 arranging a first pressure sensor with a pressure output signal and a first load cell in an investigation interval outside a wellbore conduit, wherein said first load cell includes: 
 a second pressure sensor with a stress output signal; 
 a cell element comprising a first fluid with a first fluid pressure; 
 a first interface element arranged in a first end of said first load cell with fluidly separated first and second surfaces, wherein said first surface is in fluid communication with said first fluid, and said second surface is arranged in operable communication with solid masses in said investigation interval, and said first interface element is longitudinally movable relative said cell element as a function of a first force from said sold masses applied on said first surface relative a second end opposite said first end, and said first fluid is compressible on said second pressure sensor; 
 transmitting wirelessly said stress output signal and said pressure output signal across a wall of said wellbore conduit and further via a cable inside said wellbore conduit to a surface device; 
 recording first values for said stress output signal and said pressure output signal; 
 periodically reading next values for said stress output signal and said pressure output signal; and 
 detecting a wellbore formation instability based on a difference between said next values and said first values for said stress output signal and said pressure output signal. 
 
     
     
       18. The method for determining a wellbore formation instability according to  claim 17 , comprising providing power from said surface device via a cable downhole inside said wellbore conduit and further via wireless transmission through said wall of said wellbore conduit to said investigation interval. 
     
     
       19. The method for determining a wellbore formation instability according to  claim 18  , wherein said first pressure sensor is a quartz pressure and temperature transducer, and further comprising correcting said stress output signal based on a pre-determined relation between a temperature measured by temperature sensor arranged in said investigation interval and said stress output signal. 
     
     
       20. The method for determining a wellbore formation instability according to  claim 19 , further comprising the step of initially determining said relation between said temperature measured by temperature sensor disposed in said investigation interval and said stress output signal by arranging said load cell inside a block of cement such that said cement applies said first force to said second surface, varying said temperature, and recording a variation in said stress output signal as a function of said temperature variation.